Resolution Enhancement of Extreme Ultraviolet Microscope Using an Extreme Ultraviolet Beam Splitter

We developed the extreme ultraviolet (EUV) beam splitter, which is a critical component for resolution enhancement, to achieve the uniform numerical aperture (NA) for all planar directions in the EUV microscope. In the fabrication of the EUV beam splitter, stress control of the Mo/Si multilayer is a necessary to achieve a self-standing membrane of the Mo/Si multilayer. We succeeded with the stress control by optimizing RF power, DC power, and argon working pressure during Mo/Si multilayer deposition. A large effective area of 8×10 mm2, reflectivity of 27%, and transmittance of 17% were achieved simultaneously. Furthermore, by installing the EUV beam splitter in stead of a turning mirror of Schwarzschild optics (SCO), the NA of the SCO became the same in the horizontal and vertical directions on a sample plane. Thus, the 300-nm line and space elbow pattern on an EUV mask for all planar directions was clearly resolved. We have developed an EUV microscope with an EUV beam splitter and succeeded in the highly precise pattern inspection.